Perfluoro alkylene dioxy-bis-(4-phthalic anhydrides and oxy-bis-(perfluoroalkyleneoxy-phthalic anhydrides

ABSTRACT

Novel dianhydrides having the formula:   wherein Rf is a perfluoroalkylene having the structure -CF2-n or a perfluoroalkylene ether having the structure -CF2-m-O--CF2-m wherein n is an integer of 2 to 10, and m is an integer of 1 to 10.

United States Patent [1 1 Fletcher et al.

[ Aug. 12, 1975 PERFLUORO ALKYLENE DIOXY-BIS-(4-PHTHALIC ANHYDRIDES AND OXY-BlS-(PERFLUOROALKYLENEOXY- PHTHALIC ANHYDRIDES [76] lnventors: James C. Fletcher, Administrator of the National Aeronautics and Space Administration, with respect to an invention of James A. Webster, Dayton, Ohio [22] Filed: July 16, 1974 [2]] Appl. No.: 489,008

[52] US. Cl 260/346.3; 260/78 TF; 260/520 [51] Int. Cl. C07D 307/89 [58] Field of Search 260/3463 [56] References Cited UNITED STATES PATENTS 3,310,573 3/1967 Coe 260/3463 Primary Examinerl-lenry R. Jiles Assistant ExaminerBernard I. Dentz Attorney, Agent, or Firm-W. H. Riggins; L. D. Wofford, Jr.; John R. Manning [57] ABSTRACT Novel dianhydrides having the formula:

7 Claims, N0 Drawings 'structures. The major requirement that such sealants must satisfy is the ability to maintain a seal within a fuel conditions. The conditions include exposure to high PERFLUORO ALKYLENE DIOXY-BIS-(4-PHTHALIC ANHYDRIDES AND OXY-BIS-( PERFLUOROALKYLENEOXY- Another object of the invention is to provide novel ether-linked aryl tetracarboxy anhydrides having utility 1 in the preparation of polyimides of improved fuel resis- PHTHALIC ANI-IYDRIDES tance, lowered glass transition temperature and im- 5 proved high temperature capabilities. ORIGIN OF THE INVENTION Yet another object of the invention is to provide a The invention described herein was made in the permethod for the production of the novel compounds of formance of work under a NASA contract and is subthe invention. ject to the provisions of Section 305 of the National These and other objects of the invention will become Aeronautics and Space Act of 1958, Public Law a parent from the following description and appended 85868 (72 STAT. 345; 42 U.S. I. 2457) claims.

BACKGROUND OF THEINVENTION In accordance with the present invention, there are v g I V 7 provided novel compounds of the formula:

1. Field of the Invention M O O The present invention relates to novel ether-linked aryl tetracarboxylic acids and dianhydri'des and to a O Rf 0 method for their preparation. i C '2. Description of the Prior Art H Avery definite need has developed for materials use- 0 O ful in thepreparation of sealants in advanced aerospace Rf is a perfluoroalkylene having the structure (CF or a perfluoroalkylene ether having the structure CF ),,,O-(CF wherein n is an integer of 2 to 10, preferably 4 to 6 and m is an integer of l to ID,

preferably 4 to 6.

tank for an extended period of time, normally up to 25,000 hours, while subjected to a variety of adverse and low temperatures (-45C to 260C) in the presence of oxygen, hydrocarbon fuel and moisture. These conditions necessitate a high level of thermal, oxidative and hydrolytic stability. In addition, the sealant must 1 Th compounds fth present invention may b DETAILED DESCRIPTION OF THE INVENTION also exhibit adequate physical and chemical characterpared by a series of steps comprising reacting 3,4- istics including tensile strength and elasticity, good adbis(trifluoromethyl) phenol and a perfluoroalkanedioyl hesion, and freedom from stress corrosion of titanium h lid i a ola r ti of at lea t 2 1 to rodu e th all0ys Needless to sayrthe aforementioned requirecorresponding 3,4-bis(trifluoromethyl)phenyl perts sealants for pa e are extraordinarily, fluoroalkanedioate. The 3,4-bis(triflurormethyl) phe- Ir flg lL y few are known WhiCh meet thQ nyl fluorodialkanoate is then fluorinated to produce sired properties. I r 3,3, 4,4 -tetrakis(trifluoromethyl)-a,w-diphenoxy polyfluoroalkane which is hydrolyzed to the corresponding tetracarboxylic acid. The tetracarboxylic acid thus produced is then dehydrated to the novel dianhy- SUMMARY OF THE INVENTION One object of the invention,therefore, is to provide 4 a novel compound which can be employed to prepare dride compounds of the invention. The synthesis of the polyimides exhibiting excellent thermal, oxidative and novel compounds may be outlined as follows:

H ll ()H g /()L Rl'(--() 1:, II II 2; (F

m h CF l"; "11

| ll Ill ,0 Rt (1-,, SFJHF H. 'S(),/(IS();,H D

. ll ()-Rl ()RI"- 4) c 2H..() (non 0 U [D O H()()( (non ll o o hydrolytic stability and good tensile strength and elon- 65 The perfluoroalkanedioyl halide reacted with the gation during exposure to temperatures ranging from 3,3-bis(trifluoromethyl) phenol may be any ofthe com- --C to 260C. pounds having the structure:

o ll ll where X F, Cl, Br and Rf= a perfluoroalkylene. (CF or a perfluoroalkylene ether. i.e., (CF O-(CFrhn wherein n and m are as defined above. Examples of the perfluoroalkanedioyl halide are perfluoromalonyl chloride. perfluorosuccinyl chloride, perfluoroglutaryl chloride. or fluoride, adipoyl fluoride, etc. The reaction is ordinarily conducted in the presence of an amine catalyst such as pyridine at an elevated temperature, preferably about 75C to 160C using a molar ratio of 3.4-bis(trifluoromethyl)phenol to perfluoroalkanedioyl halide of at least 2 to 1.

Fluorination of compound 111, Le, the 3,4-bis(tri fluoromethyl)phenyl perfluoroalkanedioate is effected by conventional methods known to convert carboxyl groups to CF groups. A convenient method comprises pressurizin g an autoclave containing compound III with a stoichiometric excess of sulfur tetrafluoride in admixture with anhydrous hydrogen fluoride and heating the reactant mixture at 80C 85C.

the hydrolysis of the resulting 3,3, 4,4-tetrakis (trifluoromethyl)-a, w-diphenoxy polyfluoroalkane (Compound IV) is a preferential hydrolysis of the CE, groups on the aryl ring of compound IV without attack on a perfluoroalkoxy substituent. This preferential hydrolysis may be effected by heating compound [V at temperatures of about 90C to 120C in the presence of a mixture of sulfuric acid and chlorosulfonic acid as a hydrolyzing agent.

Any of the conventional methods can be employed for conversion of the tetracarboxylic acid groups containing compound V into the dianhydride. A preferred procedure is to reflux compound V with excess acetic anhydride.

The following example will further illustrate preparation of the novel compounds of the present invention.

EXAMPLE 1 3,4-Bis(trifluoromethyl)phenol 3,4-Bis(trifluoromethyl)aniline (24 g, 0.15 mole) was dissolved in 120 ml of concentrated sulfuric acid. A solution prepared by dissolving sodium nitride 12.0 g, 0.174 mole) in 120 ml of cold concentrated sulfuric acid was added to the amine over a period of 75 minutes. The temperature was then permitted to rise to 25C and stirring was continued for 2 hours. The reaction mixture was then poured over excess ice and the resulting aqueous solution was steam distilled until 2 liters of distillate was collected. Extraction of this aqueous solution with ether and distillation of the extract afforded 19.3 g (80% yield) of 3,4-bis(trifluoromethyl)phenol, bp 116C/5O torr, 11,, 1.4286. 3,4-Bis(trifluoromethyl)phenyl Hexafluoroglutarate Pyridine catalyzed reaction of 3,4-bis(trifluoromethyl)phenol (7.8 g, 0.034 mole) with perfluoroglutaryl chloride (4.7 g, 0.017 mole) at 75 to 120C formed the corresponding diester in 90% yield, bp 155C/0. torr, V025 1.4123-28. 3',3",4, 4-Tetrakis(trifluoromethyl)-l ,S-diphenoxydecafluoropentanc A 300 stainless steel autoclave was charged with 8.0 g (0.012 mole) of 3,4-bis(trifluoromethyl)phenyl hexafluoroglutarate, 38 g 1.9 moles) hydrogen fluoride and 24 g (0.22 mole) sulfur tetrafluoride. The autoclave was heated for 3 hr at 80C and 21 hr at 85C. The

4 pressure was released after the autoclave had cooled and the contents was poured over ice and neutralized with NaHCO The product was extracted with chloroform, washed and dried. Distillation gave 8.5 g of product considered to be 3 ,3 4 ,4 tetrakis(trifluoromethyl l ,S-diphenoxydecafluoropentane, bp l15122C/0.15 torr, v 1.3895. Infrared analysis showed no carbonyl absorption.

l,5-Diphenoxydecafluoropentane-3 ,3 ,4',4 tetracarboxylic Acid A mixture of 3',3",4,4"-tetrakis(trifluoromethyl)- l,5-diphenoxydecafluoropentane (28.5 g, 0.049 mole), 100% sulfuric acid (25 g, 0.25 mole), and chlorosulfonic acid (29 g, 0.25 mole) was heated with stirring in a flask under a condenser with dry nitrogen atmosphere. The temperature was held at C for 48 hours, C for 16 hours, and C for 24 hours. During this time HCl evolved slowly. The mixture was then poured over ice, extracted with ether, washed, and dried. Evaporation of ether left a brown gummy solid. This was dissolved in 300 ml water at 85C, decolorized with charcoal, and filtered hot. Upon cooling, 19 g of white solid was collected by filtration, neut. equiv. found calcd. for tetracarboxylic acid, 153.

This product was refluxed with excess acetic anhydride and then devolatilized. Sublimation of the solid residue at 160C/ 0.01 torr afforded 17.3 g of dianhydride, mp 94-97C (60% yield).

Attempts to purify the dianhydride further by recrystallization failed for lack of a suitable solvent. The anhydride (17.3 g) was finally dissolved in water and recrystallized as the acid, mp l45l55C, neut. equiv. I59. The acid was then recrystallized from 27% (by volume) acetic acid/water solution and a second time from 35% acetic acid solution. The melting point was raised to 15ll53with very little loss in material. Neut. equiv. found 159, calcd/ 153. NMR analysis showed an equal proportion of labile and aromatic protons suggesting that the tetracarboxylic acid crystallized as the monohydrate with a calculated equivalent weight of 157.5.

The above tetraacid was then converted once again to dianhydride and sublimed. Three fractions of sublimed material were collected.

Weight mp Neut. Equiv.

g C Found C alcd.

Analysis for C H F O C H F Calcd 43.77 1.05 32.97 Found 43.53 0.96 33.10

The novel ether-linked aryl tetracarboxy dianhydride 0f the invention can be reacted with organic diamines to provide valuble polyimides having a variety of applications such asfuel tanksealants, matrix resins for composites, moldingresins, films, etc.

Condensation polymers of one diamine in particular and the compounds of the invention, however, has been found to provide-polyimides exhibiting an extraordinarily highlevel' ofthermalgoxidative and hydrolytic stability. The diamine has the structure:

wherein x and y each O to 3 and x y 0 to 3. The diamine may be prepared by the SP fluorination of the nitrophenyl ester of a perfluoroalkylene ether dicarboxylic acid, followed by catalytic reduction with hydrogen of the nitro groups to form the diamine. The 20 synthesis may be represented as follows:

The polyimide polymers produced by the polymerization of ether-linked aryl tetracarboxy dianhydrides of the invention andthe above diamine are normally solid non-crosslinked polymers comprised of repeating units having the structure:

linked aryl tetracarboxy dianhydride of the invention to the diamines dissolved in amutual solvent such as dimethylacetamide. The diamine and dianhydride reactants are employed in about. stoichiometric proportions. Small deviationsfrom 1 l proportions show little apparent changes in physical or chemical properties. In general the initial reaction to form the polyamic acid is carried out at ambient temperatures. Formation of the fluorocarbon polyamicacids takes place more slowly than with conventional polyimides, presumably because of the lower base strengths of the fluorocarbon aromatic diamines. An appreciable increase in solution viscosity becomes apparent only after stirring for over say 10-12 hours whereas with conventional polyimides 45 a maximum viscosity is normally attained within a few hours. Evaporation of solvent and heating to about 150C to 250C results in condensation of the polyamic acid to the cyclic imide.

If desired, a small proportion of a trifunctional crosslinking agent can be incorporated in the polyimide to impart high temperature mechanical stability and increased solvent resistance. The resulting crosslinked polyimides are found to exhibit high stability and appreciable tensile strength and elongation at temperatures as high as 300C. Any of the conventional trifunctional crosslinking agents for polyimides can be employed. A particularly preferred crosslinking agent is mellitic trianhydride. When used, the crosslinking agents are employed in amounts of about 2 to 20 equivalents preferably of about 5 to 15 equivalents percent based on the dianhydride employed in the polymerization.

The following examples are included to demonstrate the advantageous polyimides prepared from the novel ether-linked aryl tetracarboxy dianhydrides of the in vention. 7

EXAMPLE II l,5-Diphenoxydecafluoropentane-3 ,3 ,4',4 tetracarboxylic acid dianhydride (0.144 g, 25 millimole) was added to (0.241 g, 25 millimole) of a diamine having the following structure:

EXAMPLE III Three different polyimide preparations designated A, B and C in Table I below were prepared using the general procedure described in Example ll except that about 10 equivalents percent of the ether-linked dianhydride was replaced With mellitic trianhydride as a crosslinking agent. The polyamic acid solution for A and B was stirred 1 hour at 25C before being poured ASTM procedure D-4l 2-64T. The die dimensions, designated by the ASTM procedure as A, C, L, and W, were 8, 44, 17 and 2.6 mm, respectively.

Thetensile strength measurements carried out using microtensile test specimens approximate but may differ from values obtained using standard tensile test specimens. The reported elongation values are based on crosshead travel because of the inability to use an extensiometer. If the length of the necked-down portion of the die is considered in gauge length, the results will be too high when appreciable elongation occurs within the entire length of the specimen, between the grips. On the other hand, inspection of elongated, cold drawn specimens showed that the elongation of some specimens occurred primarily within the necked-down portion. Because of this, maximum and minimum elongation values are shown in the Table. The maximum elongation results are based on the 17 mm gauge length, and minimum values are those based on 23 mm, the specimen length between grips. The results of the tests are summarized in the following Table I.

Table l 'l'l-INSlLl'i S'l'RliNUl'H AND liLONGA'llON ()l" POLYlMlDE "Two specimens "Thruc specimens The test data demonstrate the high tensile strength and elongation at elevated temperatures possessed by the crosslinked polyimides. The properties of polymer C prepared with 2% excess anhydride were not signifi- 10 3. A compound as claimed in claim 2 wherein n is 5. 4. A method for the preparation of a dianhydride having the formula:

cantly different from polymer B. 5

0 EXAMPLE IV ll C ORf-O C The polyimide C was SLlbJCCtCd to Chevron A-SU et fuel under the conditions shown in Table II and the ten- 0 .0 sile strengths and elongations were determined before and after exposure. The results are set forth in Table 11. O 0

Table II POLYIMIDE STABILITY Tensile Polymer Strength. Elongation Ci Composition Exposure Conditions psi 17 mm gauge) C none 6 l 00 420 300 hr. 288C. fuel vapor at psiu 4500 810 (14 hr. 180C. reflux fuel. uir 4-100 730 Polymer C exposed to fuel vapor at atmospheric which comprises reacting 3,4-bis(trifluoromethyl) phepressure f 200 hours at 238C h d a i ifi no] and a perfluoroalkanedioyl halide having the strucincrease in elongation with a moderate decrease in tenture:

sile strength. Similar properties were observed after a specimen of the polyimide was refluxed in fuel for 64 hours at 180C while exposed to air.

EXAMPLE V The adhesion of films of the polyimides of Example III to stainless steel and titanium metal were investigated. The metal specimens were cleaned and then coated with the polyimide polymer composition and cured at l80C. The strips were then refluxed for 70 hours in Chevron A-SO jet fuel at 180C under a nitrogen atmosphere except for one example which was carried out in contact with air.

The results were good adhesion and resistance to refluxing jet engine fuel.

It is claimed:

1. A dianhydride having the formula:

0 l g /C O-Rf-O 0v 0 H ll wherein Rf is a perfluoroalkylene having the structure (-CF or a perfluoroalkylene ether having the structure -(CF +,,,-O-(CF wherein n is an integer of 2 to 10, and m is an integer of l to 10.

2. A compound as claimed in claim 1 wherein Rf is -(-CF and n is an integer of 4 to 6.

wherein X is selected from F, Cl and Br, Rf is -(-CF wherein n is 2-4.

6. The method of claim 5 wherein n is 3.

7. The method of claim 4 wherein the hydrolysis is conducted at about C to C in the presence of a mixture of sulfuric acid and chlorosulfonic acid as a hydrolyzing agent. 

1. A DIANHYDRIDE HAVING THE FORMULA:
 2. A compound as claimed in claim 1 wherein Rf is -CF2-n and n is an integer of 4 to
 6. 3. A compound as claimed in claim 2 wherein n is
 5. 4. A method for the preparation of a dianhydride having the formula:
 5. The method of claim 4 wherein the perfluoroalkanedioyl halide has the structure:
 6. The method of claim 5 wherein n'' is
 3. 7. The method of claim 4 wherein the hydrolysis is conducted at about 90*C to 120*C in the presence of a mixture of sulfuric acid and chlorosulfonic acid as a hydrolyzing agent.
 10. 